The present invention generally relates to batteries, e.g., electrochemical cells, and more particularly to a low profile closure assembly for closing and sealing the open end of a battery container.
FIG. 1 illustrates the construction of a conventional AA-size alkaline battery 10 utilizing a typical battery can closure assembly. As shown, conventional battery 10 includes a cylindrical-shaped steel can 12 having an open top end 14, a closed bottom end 16, and side walls extending between the top and bottom ends. The closed bottom end 16 of steel can 12 includes a protruding nub 18 formed at its center region and contacting the steel can 12 to serve as the positive contact terminal of battery 10.
The conventional battery 10 shown is an electrochemical cell further having a positive electrode material 20, commonly referred to as the cathode, which comprises manganese dioxide as the active material. The cathode 20 may be preformed and inserted into steel can 12, or may be molded in place, so as to contact the inner surface of can 12. After the positive electrode 20 has been provided in steel can 12, a separator 22 is inserted into the space defined by the interior walls of the positive electrode 20. Separator 22 is typically made of a non-woven fabric and serves to provide physical separation between the positive electrode 20 and a negative electrode 24. The negative electrode 24, commonly referred to as the anode, is centrally disposed in the steel can 12 and comprises zinc powder as the active material. An alkaline electrolyte, a solution of aqueous potassium hydroxide (KOH), is further disposed in the steel can 12.
Once the electrodes 20 and 24, separator 22, and alkaline electrolyte have been disposed inside steel can 12, a preassembled collector assembly is inserted into the open end of steel can 12. To accommodate the insertion of the collector assembly, the steel can 12 is typically either slightly flared at its open end 14 or includes an inwardly extending bead or step to support the collector assembly in a desired orientation. The conventional collector assembly includes a current collector nail 26, a nylon seal 28, an inner metal cover 30, and an outer metal cover 32. The current collector nail 26 extends into the anode 24 and has an enlarged head that is welded or otherwise in electrical contact with outer metal cover 32. Current collector 26 extends through an opening formed in a central hub 34 of seal 28. The inner cover 30, which is formed of rigid metal, is disposed between the central hub 34 and peripheral upstanding wall 36 of seal 28 to increase the rigidity and support the radial compression of the collector assembly, thereby improving the sealing effectiveness. By configuring the collector assembly in this fashion, the inner metal cover 30 serves to enable compression of the central hub 34 against current collector 26, while also supporting compression of the peripheral upstanding wall 36 of seal 28 against the inner surface of the steel can 12.
After the collector assembly has been inserted in the open end 14 of can 12, the assembly is secured in place by radially squeezing the side walls at the open end 14 of the steel can 12 inward against the collector assembly and outer cover 32, and crimping the open end edge of the can 12 over the peripheral lip of the collector assembly and outer cover 32 to secure the outer cover and collector assembly within the open end of the can 12. Thereafter, a metalized, plastic film label 38 is formed about the exterior surface of steel can 12, except the ends of steel can 12. Label 38 is formed over the peripheral edge of the bottom end 16 of can 12 and partially extends onto the outer negative cover 32.
The conventional crimping process bends the open end of the can 12 ninety degrees onto the outer cover 32 and, in doing so, subjects the can 12 to an axial load. In order to withstand the conventional crimping of the can over the collector assembly, the steel can 12 must be strong enough to prevent can deformation, such as buckling of the side walls at the bottom of the can, which is caused by the axial compression forces that are typically experienced during the crimping operation. To withstand the axial load during crimping, the conventional AA-size battery typically requires a steel can having a thickness of about ten mils.
Although the above-identified collector assembly performs all the above-noted desirable functions satisfactorily, as apparent from its cross-sectional profile, this particular collector assembly and the steel can occupy a significant amount of space within the interior of the battery 10. Because the exterior dimensions of the battery are generally fixed by the American National Standards Institute (ANSI), the greater the space occupied by the steel can 12 and collector assembly, the less space that there is available within the battery 10 for the electrochemical materials. Consequently, a reduction in the amount of electrochemical materials that may be provided within the battery results in a shorter service life for the battery. It is therefore desirable to maximize the interior volume within a battery that is available for the electrochemically active components. It is further desirable to construct a battery so that the space occupied by the collector assembly and the space occupied by the battery can are minimized, while still maintaining adequate sealing characteristics. It is yet further desirable to minimize axial load applied to the battery can during can closure.
The present invention allows for the use of a thinner gauge can which increases the volume available for active materials in a battery. Another aspect of the present invention provides a collector assembly that effectively seals the open end of the battery container with enhanced manufacturability, reduced cost, and improved current collector alignment. To achieve these and other advantages, and in accordance with the purpose of the invention as embodied and described herein, the present invention provides for a battery employing a container having a bottom end, an open top end, and side walls extending between the top and bottom ends. Positive and negative electrodes are disposed in the container. An outer cover is disposed over the open end of the container. The outer cover has an outer flange extending on the outside of the container side walls and an inner flange extending on the inside of the container side walls. A seal is disposed between the container and the outer cover so that the seal is disposed against the inner and outer flanges of the outer cover. The outer cover is preferably crimped against the container side walls to compress the seal between each of the inner and outer flanges and the container.
According to another aspect of the present invention, a method of assembling a battery is provided. The method includes forming a container having an open top end, a bottom end, and side walls extending between the top and bottom ends. The method also includes forming a cover having an outer peripheral flange and an inner flange, with a channel provided therebetween. The method further includes dispensing active battery materials in the container, and placing the cover over the open top end of the container so that the outer and inner flanges are on opposite sides of the container side walls and the container and outer cover are separated by a seal. The method further includes forcing the outer and inner flanges of the outer cover against the seal so as to compress the seal between the container and the outer cover.
The resultant closure assembly advantageously provides for a simplified technique for closing the open end of the battery can, while providing enhanced sealing and allowing for a reduced thickness can due to minimal axial closing forces. Accordingly, the battery may employ a thinner battery can, as compared to conventional battery cans.